When I open a new session, I put the mouse on the Avast! bowl. Most of the time, a short message appears: “5 providers, 4 running” (or something like that, I have Avast! in French).
From time to time, there are only « 4 services, 3 en exécution) » (4 providers, 3 running). Then, I know Avast! will not work properly : it will allow any incoming mail, virus-free or not. I have to restart my PC. :(.
You can change the installed providers at Control Panel > Add/Remove applet > avast antivirus > Remove … choose ‘Change’ in the new window that pop up and check the desired providers.
If you open avast settings you can check all the ‘Confirmations’ (i.e., bring back avast to the default confirmations settings) and choose ‘keep’ the behavior after you change the provider state. In other words, you may be able to choose if you want the provider is ‘off’ or ‘on’ on next boot. That should work I hope.